Impact of Substrate and Process on the Electrical Performance of Screen-Printed Nickel Electrodes: Fundamental Mechanism of Ink Film Roughness

In recent years, traditional printing methods have been integrated to print flexible electronic devices and circuits. Since process requirements for electronics differ from those for graphic printing, the fundamentals require rediscovery mainly to optimize manufacturing techniques and to find cost reduction methods without compromising functional performance. In addition, alternative inks need to be formulated to increase the variety of functional inks and to pioneer new product developments. In this report, we investigate a thermoplastic-based nickel ink prototype to print electrodes using a screen-printing process. Process fundamentals are explored, and cost reduction methods are addressed by studying the effect of substrate roughness, print direction, and number of ink layers on the electrical performance of printed nickel. Multilayered electrodes are printed on paper and heat stabilized engineered film. A novel fundamental mechanism is found that explains the effect of substrate roughness on ink film roughness in screen printing, including the roughness measurement of the screen mesh wire that is reported for the first time. Results demonstrated that (i) surface roughness of substrates does not have significant effect on printed ink film roughness in screen printing; (ii) ink film thickness is higher on nonabsorbent materials, while line gain is higher on absorbent materials; (iii) the effect of electrode orientation on electrical performance is insignificant; and (iv) the effect of substrate roughness on the electrical performance for the first print layer can be eliminated by printing multiple layers. The results significantly affect substrate choice and number of ink layers, which are considered the major cost factors in the manufacturing of printed electronics.